Prepare a grill for medium-high heat or heat a grill pan over medium-high; oil grate or pan. Grill steaks and remaining pineapple rounds, turning occasionally, until pineapple is lightly charred and an instant-read thermometer inserted into the center of steak registers 120°F, 8–10 minutes for medium-rare (pineapple may take longer to cook than steak).

Transfer steak to a cutting board. Let sit at least 15 minutes, then thinly slice. Transfer pineapple to a platter and tent with foil to keep warm.

Cut avocados in half crosswise around pit, then carefully peel off skin with your hands. Slice each half crosswise into 1/2" rings.

Arrange sliced steak and avocado on platter with pineapple. Drizzle with pineapple dressing; season with salt and pepper.